A requirement in both still and full motion imaging systems or beam director systems is a stable optical axis so that no image degradation or beam motion occurs during scene sampling or beam emission. As optical magnification increases the optical axis stabilization performance requirements increase proportionally. Systems using the highest available magnification to meet the system design requirements correspondingly require the highest performance stabilization systems. In the general case, these stabilization systems are characterized by four or five axis gimbal designs requiring high volume, power, weight, complexity, and cost. An alternative stabilization approach uses a lower order two axis gimbal design with a beam steering element inserted into the optical path of the imaging system. The two axis gimbal uses inertial rate feedback to provide coarse stabilization of the optical axis just as the higher order gimbals. The residual inertial error is then further acted upon by the fine stabilization beam steering process to reject the remaining optical axis deflections and minimize the net residual inertial pointing error. Such a design solution has been successfully implemented and in many cases provides stabilization performance equivalent to or even exceeding that of the higher order gimbal design solutions.
To date the alternative stabilization approach at best can achieve an order of magnitude improvement over a limited frequency region on the coarse two axis gimbal set residual stabilization error. This limitation is a result of the response achieved to date of the beam steering element control methodology.